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Detectionmediumtest

Suspicious FromBase64String Usage On Gzip Archive - Process Creation

Detects attempts of decoding a base64 Gzip archive via PowerShell. This technique is often used as a method to load malicious content into memory afterward.

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Launch
François HubautCreated Fri Dec 23d75d6b6b-adb9-48f7-824b-ac2e786efe1fwindows
Log Source
WindowsProcess Creation
ProductWindows← raw: windows
CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic
Detection Logic1 selector
detection:
    selection:
        CommandLine|contains|all:
            - 'FromBase64String'
            - 'MemoryStream'
            - 'H4sI'
    condition: selection
False Positives

Legitimate administrative script

References
1
Resolving title…
speakerdeck.com
MITRE ATT&CK
Related Rules
SimilarDetectionmedium

Suspicious FromBase64String Usage On Gzip Archive - Ps Script

Detects attempts of decoding a base64 Gzip archive in a PowerShell script. This technique is often used as a method to load malicious content into memory afterward.

Detects similar activity. Both rules may fire on overlapping events.

Rule Metadata
Rule ID
d75d6b6b-adb9-48f7-824b-ac2e786efe1f
Status
test
Level
medium
Type
Detection
Created
Fri Dec 23
Author
François Hubaut
Path
rules/windows/process_creation/proc_creation_win_powershell_frombase64string_archive.yml
Raw Tags
attack.command-and-controlattack.t1132.001
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